Flush-mounted plural waveguide slot antenna



April 25,1961 R. s. ELLIOTT MOUNTED PLURAL WAVEGUIDE SLOT ANTENNA FLUSH- Filed Sept. 4, 1956 2 Sheets-Sheet l //V VE N 701?.

A T TOR/V5 Y.

April 25, 1961 R. s. ELLIOTT FLUSH-MOUNTED PLURAL WAVEGUIDE SLOT ANTENNA Filed Sept. 4, 1956 2 Sheets-Sheet 2 Robert S. Elliott,

nvvsmrom A 7' TORNE Y.

FLUSH-MOUNTED PLURAL WAVEGUIDE SLOT ANTENNA Robert S. Elliott, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Sept. 4, 1956, Ser. No. 607,830 6 Claims. (Cl. 343-771) This invention relates to beacon antennas and more particularly to a flush-mounted antenna of the end-fire type adapted either to radiate a toroidal beam or to scan a toroidal region.

Heretofore, it has been proposed to produce a toroidal beam by means of an isolated half-wave antenna. Such a half-wave antenna has the disadvantage of giving rise to a very broad beam in the elevation plane making the resulting radiation pattern unsuitable for many applications which required a large gain. To increase the sharpness of the elevation pattern of toroidal beams, biconical horns have been used with success. However, when low aerodynamic drag is required in addition to a large antenna gain, biconical horns are also unsuitable. Recently, center-fed annular corrugated surface antennas have found application when aerodynamic requirements demanded a flush-mounted antenna structure. This has been described in a paper entitled An Annular Corrugated-Surface Antenna, by E. M. T. Jones, published in The Proceedings of the IRE, June 1952, vol. 40, No. 6, page 721. Even though the aerodynamic characteristics of such an antenna are excellent, the inherently limited degree of beam shaping and gain control in the elevation plane which such an antenna is capable of have restricted its application considerably. Further, annular corrugated surface antennas as well as many other beacon antennas employing trapping means to provide surface waves, lack a certain degree of versatility in that such antennas are primarily suitable to generate a toroidal beam pattern and are not readily adapted for scanning a beam through a toroidal region.

It is therefore an object of this invention to provide a flush-mounted beacon antenna of the end-fire type having a predetermined elevation pattern which pattern is not inherently limited in gain but readily adjustable to any degree of sharpness desired.

It is a further object of this invention to provide a versatile flush-mounted beacon antenna which is capable of either producing a fixed toroidal beam or of scanning a beam through a toroidal region.

It is a still further object of this invention to provide a new type of end-fire antenna which has a low aerodynamic drag, a high gain predetermined elevation pattern and which is rugged in construction and which may also be made to scan.

In accordance with this invention a set of identical sectoral waveguides is arranged side by side to form a circular body henceforth referred to as the antenna, having a thickness equal to that of the waveguides Electromagnetic wave energy is fed to the sectoral waveguides from a central position of the antenna so that propagation takes place from the narrow opening of the sectoral waveguide in the direction of increasing radius. The wide opening of the sectoral waveguides is capped and one of the parallel walls of the waveguide is provided with a radiation aperture in the form of serrations. Wave energy leaks out of the sectoral waveguides through the serrations to provide an end-fire beam in the direction of wave propagation, a phenomena well known to those skilled in the art.

When all sectoral waveguides are fed simultaneously, an omnidirectional or toroidal beam is obtained. When United States Patent Patented Apr. 25, 1961 feeding less than all the waveguides at the same time, a directional beam in the azimuth plane may be provided. Therefore, by progressively feeding adjacent sectoral waveguides a progressively sweeping or scanning beam may be obtained, the width of the beam in the azimuthal plane depending on the number of waveguides fed at any one instant of time.

Fig. 1 is a perspective exploded view of an embodiment of the flush-mounted beacon antenna provided in accordance with this invention;

Fig. 2 is a fragmentary top plan view of two adjacent radial waveguides showing the position of the serrations of the flush mounted beacon antenna of Fig. 1;

Fig. 3 is a cross-sectional fragmentary view and Fig. 4 is a sectional view taken along line 44 of Fig. 3 of a coaxial waveguide feed system for the antenna of Fig. 1;

Fig. 5 is an electric field vector diagram showing the mode transition from the coaxial waveguide feed to the sectoral waveguides of the feed structure of Fig. 3;

Fig. 6 is a cross-sectional fragmentary view, and Fig. 7 is a sectional view taken along line 7-7 of Fig. 6 of a scanning radial waveguide feed for the antenna of Fig. 1; and

Fig. 8 is a cross-sectional fragmentary view and Fig. 9 is a sectional view taken along line 9-9 of Fig. 8 of a scanning horn waveguide feed for the antenna of Fig. l.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Referring now to the drawings and more particularly to Figs. 1 and 2 there is shown a flush-mounted beacon antenna 10 in accordance with this invention. The antenna 10 comprises essentially a metallic lower plate 12, a metallic upper plate 14 and a metallic cylindrical shell or rim 16 all of which are symmetric with respect to an antenna axis 18. The upper plate 14 and the cylindrical shell 16 together form a cover 20.

The lower plate 12 is provided with a number of radial planar fins 22 which serve to divide the space between the lower plate 12 and the cover 20 into a number of identical sectoral spaces 24. The outer end portions 26 of the fins 22 are shown to extend to the edge 28 of the lower plate 12 so that upon assembly of the cover 20 with the lower plate 12 the end portion 26 abuts against the inner edge of the cylindrical shell 16. The inner end portions 27 of the fins 22 form a cylindrical space 29 about the antenna axis 18. The lower plate 12 may be supported by a hollow support 30 or any other suitable support means. The cylindrical space 29 is provided with a central feed opening 32 in the lower plate 12 to allow access to a feed means. The upper plate 14 contains a large number of narrow, closely spaced non-resonant slots 33 which are arranged in groups, each of the groups being associated with one of the sectoral spaces 24. Said groups of slots are known in the art as serrations.

Whereas the antenna 10 has been described as being made up of components such as the lower plate 12, the upper plate 14, and the rim 16, such components are merely structural details of one embodiment. Electrically and therefore basically, the antenna 10 comprises a radial waveguide which is radially subdivided starting at a predetermined radial distance by means of the fins 22 into a number of identical sectoral waveguides 24 each of which has a sectoral waveguide axis 25. Wave energy is supplied to the individual sectoral waveguides through their throats and radiated therefrom via serrations.

The sectoral waveguide 24 as shown particularly in Fig. 2 has two parallel top and bottom walls 38 and 40, two flared side walls 22, a throat or input port 36 and a mouth 42. The mouth 42 is closed electrically to prevent the escape of wave energy therefrom. Such a closure member is illustrated by the cylindrical shell 16 and may conveniently be replaced by any conductive wall inserted between the parallel top and bottom walls 38 and 40 and the two flared side walls 22. The throat or input port 36 of the sectoral waveguide 24 has a width A which may have any value as long as it is greater than one-half of the wavelength of the wave energy propagated by the sectoral waveguide 24.

Exchange of wave energy between the sectoral waveguides 24 and free space takes place through the serrations 34. Serrations have a very similar effect as an open or leaky waveguide permitting a leaking oil of the wave energy from the sectoral waveguide 24 into space in the form of an end-fire beam. The elevation pattern of such an end-fire beam depends on the relative amplitudes and phases of the wave energy contributed by each slot. Since the position of the individual slot fixes the phase of its contribution, the amplitude of each contributing wave may be controlled by adjusting the length of the individual slot. As shown in Fig. 2, the line 44 defining the aperture 34 is the generatrix of all the slot termini and its shape determines the elevation pattern of the end-fire beam. The beam angle itself may be raised or lowered by properly increasing or decreasing the curvature of the parallel top and bottom sides of the sectoral waveguides. Fig. 1 shows the curvature of the lower and upper plates 12, 14 to be parabolic and depending upon the desired beam angle, this curvature may be spherical, hyperbolic or conical. In other words, the elevation pattern, as well as the beam angle may be controlled by changing the length of the slots 33 relative to one another and by changing the curvature of the sectoral waveguides.

The antenna of Fig. 1 may be provided with wave energy feed means adapted to excite and be excited by one or more of the sectoral waveguides 24 either progressively or simultaneously depending on whether an omnidirectional or a scanning beam is desired. As is well known in the art, a sectoral waveguide will propagate the TE -mode of a rectangular waveguide so that any feed means extending over the region of coincidence with the throat of the sectoral waveguide 24 must be adapted to excite and be excited by such a mode.

To obtain an omnidirectional beam, also called a toroidal beam, all of the sectoral waveguides 24 of the antenna 10 are excited simultaneously and in phase with one another. For scanning a wave energy beam through a toroidal sector, the sectoral waveguides 24 of antenna 10 are excited progressively or sequentially and the number of waveguides excited at any instant of time will determine the azimuthal pattern of the radiated beam. Consequently, in order to obtain sharpness in the azimuthal plane, it is usually desirable to excite at least two and preferably three or four sectoral waveguides simultaneously.

Fig. 3 shows an embodiment of wave energy feed means adapted to excite all of said sectoral waveguides 24 simultaneously thereby to produce a toroidal beam. The lower plate 12 together with the upper plate 14 and the fins 22 define the sectoral waveguides 24. The lower plate 12 is supported by the hollow support member 30 which permits the axial positioning and coupling of a coaxial waveguide feed 50 to the antenna of Fig. l. The coaxial waveguide feed 50 comprises an outer conductor 52 and an inner conductor 54. The outer conductor 52 is coupled to the feed opening 32 in the lower plate 12 while the inner conductor 52 is coupled to the upper plate 14 as shown.

The relative position and symmetry of the fins 22 forming the sectoral waveguides 24 and the coaxial feed waveguide 50 is shown particularly in Fig. 4. It also shows the existence of the cylindrical space 29 terminated by the end portions 27 of the radial fins 22 which space is electrically equivalent to a radial waveguide.

For the purpose of illustrating the method of operation of the feed means of Figs. 3 and 4, it is helpful to look at the wave energy mode transformation from the coaxial waveguide 50 to the sectoral waveguide 24. Fig. 5 shows diagrammatically the progressive mode change of the electric field vector E. The circular cylinder 29 defined by the throats of the sectoral waveguides 24 may be likened to a radial waveguide which separates the coaxial waveguide 50 from the sectoral waveguide 24. Wave energy in the principal TEM-mode of the coaxial waveguide 50 enters the radial waveguide 29 and excites the principal TEM-mode of the radial waveguide therein. This is shown by the change of the electric field vector E from a horizontal plane to a vertical plane. The radial waveguide 29 propagates the principal mode radially and equally towards the edge 27 of the sectoral waveguide 24. As the electric vector E is perpendicular to the parallel walls 38 and 40, the sectoral waveguide 24 will be excited in its dominant mode.

Figs. 6 and 7 show an embodiment of a wave energy feed means for the antenna 10 of Fig. l which is suitable for scanning a wave energy beam through a toroidal sector. The lower plate 12, the upper plate 14 and the fins 22 form the sectoral waveguides 24. A coaxial waveguide feed 60 has its inner conductor 62 coupled to the center of the upper plate 14. The outer conductor 64 is rigidly connected to a radial waveguide 66 which is provided with an opening 68 in its cylindrical wall 70. The outer conductor 64 together with appended radial waveguide 66 is rotatably mounted with respect to the sectoral waveguides 24 defining the beacon antenna 10 of Fig. 1. A motor 72 is coupled to the outer conductor 64 by a train of gears 74 providing rotation means to the radial waveguide 66. To minimize impedance mismatches across the gap 76 formed between the radial waveguide 66 and the lower plate 12, it has been found convenient to provide a choke coupling 78 across the gap. The choke coupling 78 may be fixed to the lower plate 12 permitting the outer conductor 64 to rotate with respect to the choke coupling 78. The width of the opening 68 must be greater than one-half of the operating wavelength within the sectoral waveguide 24 and is usually made large enough to excite two or three sectoral waveguides 24 simultaneously. As mentioned before, the directivity of the azimuth pattern is related to the number of sectoral waveguides excited simultaneously.

Figs. 8 and 9 show still another embodiment of a wave energy feed means for the antenna 10 of Fig. 1 suitable to provide a wave energy beam scanning through a sectoral sector. Whereas the embodiments of the wave energy feed means shown in Fig. 3 and Fig. 6 required the interposition of a radial waveguide between the coaxial waveguide feed and the sectoral waveguides, the wave energy feed means of Fig. 8 supplies wave energy directly to the sectoral waveguides without any mode transformation. The sectoral waveguides 24 are formed again by the lower plate 12, the upper plate 14 and the fins 22. A rectangular waveguide 80 is provided with a degree bend 82 to which is afiixed an H-plane sectoral horn 84. The waveguide 80 is rotatably mounted along the antenna axis 18 and may be rotated about its axis by a motor 86 coupled to the waveguide 80 by a train of gears 88 to produce a scanning beam. The width of the mouth 90 of the sectoral horn 84 will determine the number of sectoral waveguides 24 fed simultaneously and therefore is determinative of the directiveness of the azimuthal pattern of the scanning beam.

There has been described a flush-mounted beacon antenna in accordance with this invention which provides a stationary or scanning end-fire wave energy beam. The

aerodynamic body thereby providing a dragless beacon antenna.

What is claimed is:

1. An antenna adapted to be flush-mounted comprising: a plurality of identical sectoral waveguides, each defining a sectoral waveguide axis and each being adapted to propagate the TE -mode, said waveguides being disposed with radial symmetry about an antenna axis so that all of said sectoral waveguide axes lie in a surface of revolution and intersect said antenna axis at a common point, each of said sectoral waveguides having a throat, a mouth and a pair of parallel walls, each of said mouths of said sectoral waveguides being provided with capping means to prevent wave energy escaping therefrom, one of said parallel walls of each of said sectoral waveguides being provided with radiation aperture means to effect an exchange of wave energy between said sectoral waveguides and free space in the form of an end-fire beam, a radial waveguide adapted to propagate the dominant TEM-mode and terminated by a cylindrical wall, said cylindrical wall having a aperture equal in width to at least one of said sectoral waveguide throats, said radial waveguide being mounted rotatably about said antenna axis to provide coincidence of said aperture with at least one of said sectoral waveguide throats, a coaxial waveguide feed coupled centrally to said radial waveguide, and rotating means coupled to said radial waveguide, whereby said aperture is brought sequentially into coincidence with a different one of said sectoral waveguides, thereby providing scanning of the wave energy beam through a sectoral sector.

2. A beacon antenna adapted to be flush-mounted comprising: a plurality of identical sectoral waveguides, each defining a sectoral waveguide axis and each being adapted to propagate the TE -mode, said waveguides being disposed with radial symmetry about an antenna axis so that all of said sectoral waveguide axes lie in a surface of revolution and intersect said antenna axis at a common point, each of said sectoral waveguides having a throat, a mouth and a pair of substantially parallel walls, each of said mouths of said sectoral waveguides being provided with capping means to prevent wave energy escaping therefrom, one of said parallel walls of each of said sectoral waveguides being provided with a radiation aperture to effect an exchange of wave energy between said sectoral waveguides and free space in the form of a radially directed end-fire beam, a rectangular waveguide adapted to excite and be excited by wave energy in the dominant TE -mode mounted rotatably about said an tenna axis, said rectangular waveguide having a 90- degree bend at one end thereof, an H-plane sectoral horn having a horn mouth coupled to said bend, said horn mouth being equal in width to at least two of said sectoral waveguide throats, and means for rotating said rectangular waveguide, whereby said horn mouth is sequentially brought into coincidence with the throats of different ones of said sectoral Waveguides.

3. An antenna comprising: a pair of substantially parallel walls spaced from each other to form a volume of revolution, a plurality of radial walls disposed between said parallel walls to divide said volume into a plurality of sectoral waveguides having restricted radially inner ends for the passage of electromagnetic energy therethrough and having enlarged radially outer ends termimated to prevent the passage of energy therethrough, at least one of said parallel walls having a separate group of slots for each of said sectoral waveguides, the slots in each of said groups being arranged to couple energy be tween said sectoral waveguides and free space whereby each of said sectorial waveguides will have a predetermined pattern that extends substantially radially outwardly therefrom.

4. An antenna adapted to be mounted substantially flush with a surrounding surface, said antenna comprising a first wall adapted to be disposed substantially flush with said surface, a second wall disposed in said spaced parallel relation to said first wall to form a volume of revolution therebetween, a plurality of walls radially disposed between said parallel walls to form a plurality of sectoral waveguides, each of said sectoral waveguides having a restricted throat and an enlarged mouth, input means coupled to said throats of said sectoral waveguides for causing electromagnetic energy to be propagated therethrough, means for terminating each of said enlarged mouths to prevent the escape of said energy therethrough, a separate group of slots through said first plate for each of said sectoral waveguides, the slots in each of said groups being arranged to cause the energy in the associated waveguide to be coupled therethrough and propagated radially outwardly through space in a predetermined pattern.

5. An antenna comprising a pair of substantially parallel walls spaced from each other to form a volume of revolution, a plurality of radial walls disposed between said parallel walls to divide said volume into a plurality of sectoral waveguides having restricted radial inner ends and enlarged radial outer ends, means for sequentially feeding electromagnetic energy through preselected ones of said inner ends and into said sectoral waveguides, terminating means at each of said outer ends for preventing the loss of said energy in said waveguides through said enlarged ends, at least one of said parallel walls having a separate group of slots for each of said sectoral waveguides, the slots in each of said groups being arranged to couple energy out of said sectoral waveguides so as to be propagated radially outwardly in predetermined patterns.

6. An antenna adapted to be mounted substantially flush with a surrounding surface, said antenna comprising a first wall adapted to be disposed substantially flush with said surface, a second wall disposed in spaced parallel relation thereto to form a volume of revolution therebetween, a plurality of walls radially disposed between said parallel walls to form a plurality of sectoral waveguides, each of said sectoral waveguides having a restricted throat and an enlarged end, waveguiding means disposed adjacent said throats for sequentially feeding electromagnetic energy through preselected throats and into the associated sectoral waveguides, terminating means at each of said enlarged ends for preventing the loss of said energy in said sectoral waveguides therethrough, a separate group of slots through said first plate for each of said sectoral waveguides, the slots in each of said groups being arranged to cause the energy in the associated sectoral waveguide to be coupled therethrough and propagated radially outwardly through space in a pattern substantially coplanar with said surface.

References Cited in the file of this patent France June 25, 1952 

